I'm trying to understand the receptive fields of CNN better. To do that I would like to calculate the receptive field of each neuron in LeNet. For a normal MLP it's rather easy (see http://deeplearning.net/tutorial/lenet.html#sparse-connectivity), but it's more difficult to calculate the receptive field of a neuron in a layer following one or more convolutional layers and pooling layers.
What is the receptive field of a neuron in the 2. convolutional layer? How much bigger is it in the following subsampling/pooling layer? And what is the formula for calculating these?